How do you calculate ratios for industries and sectors on your website?

The industry, sector and S&P 500 numbers on the Ratios page are market capitalization-weighted averages of all the companies in those groups. Industries and sectors are determined by a company's placement in the Reuters Business Sector Schema, (RBSS) while the components of the S&P 500 are determined by Standard and Poors and can be found at their Web site. These averages may or may not correspond to those numbers reported elsewhere in Reuters or as presented by other data providers.